Leak detector



Aug- 23, 1955 R. F. WEHRMANN ET AL 2,716,229

LEAK DETECTOR Filed June 14, 1946 United States Patent O LEAK DETECTOR RalphF. Wehrmann, Dayton, 0hio, and Elmer W. Rebol, Richland, Wash., assignors to the United States of America'- as represented by the United: States Atomic Energy Commission Applicationune 14, 1946, Serial No. 676,602

2 Claims. (Cl. 340-242) This invention relates to an electrical indicating system and to apparatus employed therein. More particularly the invention relates to means for detecting expansion of confined bodies.

ln neutronic reactors of the liquid cooled type described in the application of Enrico Fermi and Leo Szilard, Serial No. 568,904, filed December 19, 1944, uranium cylinders are disposed in a plurality of tubes that are ribbed internally to support the uranium and to provide a space for cooling water to flow through the tubes and around the uranium. The uranium is generally loaded into the water tubes in a plurality of short cylindrical sections that are hermetically sealed in aluminum jackets to protect the highly corrodable uranium from the cooling water. In view of the large number of such short individually jacketed uranium bodies employed in a single neutronic reactor, there is a chance that one or more of the bodies may leak and permit water to come in contact with the uranium. The resultant uranium hydride has a much greater volume than the metal and will cause swelling of the aluminum jacketed uranium body.

It is desirable to employ an alarm system to detect initial swelling of the jacketed uranium bodies in order that they may be removed before the swelling has progressed to the point where removal of the bodies from the cooling water tube becomes diicult or impossible.

An object of the invention is to provide apparatus for indicating change in shape or swelling of material disposed through the length of a tube.

Another object is to provide an elongated contactor that is sensitive to pressure at any point along its length.

Another object is to provide means for constructing such an elongated contactor.

Other objects will be apparent from the specilication and accompanying claims taken together with the drawing, in which:

Fig. l is a sectional view through a coolant tube containing a jacketed uranium body as employed in certain neutronic reactors;

Fig. 2 is a partly diagrammatic View of an electrical alarm circuit and shows the disposition of the special contactor in a sectional View of a fragment of a neutronic reactor coolant tube; and

Fig. 3 is a section through one form of contactor contemplated by this invention.

In carrying out the object of detecting the swelling of jacketed uranium bodies in the cooling tubes of a neutronic reactor, an elongated contactor is disposed between the cooling water tube and the jacketed uranium bodies within the space occupied by the cooling water. Any swelling of a uranium body will exert a force on the contactor to complete an electrical circuit and energize a suitable alarm.

In its simplest form the contactor may consist of a metal wire having a relatively thick insulating oxide coat. For example, an aluminum wire anodized in oxalic acid for suiiicient time is found to have an oxide coat of suffi- ICC cient thickness to provide good electrical resistance. The insulation thus provided is suciently frangible to failv under pressure applied due to swelling of the jacketed uranium body so that the aluminum wire will become exposed and will complete an electrical circuit with the cooling water tube.

Figs. l and 2 show such an oxide coated wire 10 disposed in an aluminum cooling water tube 12 of a neutronic reactor. The tube 12 is provided withlongitudinal ribsf14 that support a cylindrical uranium body 16 coaxially with the cooling water tube 12. The uranium body 16 is encased in a thin aluminum jacket 18 that normally prevents cooling water from coming in contact with the uranium. The wire 10 preferably is of such diameter that very slight swelling of the uranium body 16 will squeeze the wire 10 against the tube 12. Due to the frangibility of the oxide coat on the Wire 10, the wire becomes an electrical contactor that completes a circuit on application of pressure to the oxide coat.

The wire 10 is electrically connected to a current source 20, the other terminal of which is connected to the cooling water tube 12 through a switch 22, safety resistance 24 and an ammeter 26. Alternatively a suitable alarm, such as a bell, could be substituted for the switch, resistance and ammeter to provide a constant check on possible swelling of the uranium bodies.

An alternative contactor is illustrated in Fig. 3. Here an anodized aluminum wire 30 having an oxide coating 32 has been drawn into a thin walled aluminum tube 34. This contactor is used in the same way as that previously described with the exception that the water tube is not used as part of the electrical circuit. The circuit is completed between the wire 30 and the tube 34 and electrical connections are made directly to these elements. This structure has the advantage that the oxide coat is not subject to damage due to abrasion in handling.

A preferred method of coating aluminum wire is to anodize it in a 3 per cent oxalic acid bath at room temperature for 30 minutes at 50 volts D. C. The wire in this case was of 0.037" diameter. Another method of obtaining an oxide coating giving good results was similar to the above method but employed a 3 per cent CrOs solution with current at 50 volts D. C., and another method employed at l5 per cent H2804 solution with current at l5 volts D. C. These oxide coatings were found to provide good electrical resistance and were sufiiciently frangible to function in accordance with the requirements outlined above.

It will be understood that other combinations of metals and insulating coatings could be substituted for those herein described without departing from the spirit of the invention. The scope of the invention is, therefore, to be limited only by the appended claims.

What is claimed is:

l. A device for detecting leaks in the jacket of a jacketed uranium body comprising, in combination, an electrically conducting sleeve adapted to tightly contain the jacketed uranium body, water disposed within the sleeve adapted to surround the jacket of the uranium body, an aluminum wire disposed adjacent to one of the surfaces of the electrically conducting sleeve, in contactual relationship with the sleeve, said wire having a coating of aluminum oxide insulating the wire from adjacent materials, and means to detect breakdowns in the electrical insulation between the wire and the sleeve, whereby leakage of water through the jacket of the jacketed uranium body produces a chemical reaction between the water and uranium producing a sol-id product of larger volume than the uranium and crushes the aluminum oxide coating on the aluminum wire to break down the electri- 2. A device for detecting leaks in the jacket of a jacketed body comprising, in combination, an electrically conducting sleeve, a fluid disposed within the sleeve which is chemically inert with the jacket and chemically active with the body within the jacket, the reaction forming a solid product of larger volume than the body, and an electrically conducting element provided with a coating of frangible insulating material disposed within and adjacent to the sleeve, the jacketed body being adapted to t snugly within the sleeve in contactual relationship with the electrically conducting element, whereby leakage of the uid through the jacket of the jacketed body causes swelling of the jacketed body and rupturing of the frangible insulating material on the electrically conducting element, thus increasing the electrical conductivity between the electrically conducting element and the electrically conducting sleeve.

References Cited inthe le of this patent UNITED STATES PATENTS 2,105,286 Jennings Jan. 11, 1938 2,166,139 Guthrie et al July 18, 1939 2,326,557 Pierce Aug. 10, 1943 2,432,367 Andresen Dec. 9, 1947 2,463,765 Grouse et al Mar. 8, 1949 

